Jr. Mcelhanon et Dv. Mcgrath, CONSTITUTION, CONFIGURATION, AND THE OPTICAL-ACTIVITY OF CHIRAL DENDRIMERS, Journal of the American Chemical Society, 120(8), 1998, pp. 1647-1656
Three series of zeroth to second generation chiral dendrimers, 7-9, 10
-12, and 13-15, were prepared by convergent methods using chiral, nonr
acemic AB(2) monomers 1, 2, and 3, respectively. Chiroptical data reve
aled a significant change in molar rotation per subunit ([Phi](D)/n) a
s dendrimer generation increased for dendrimers 7-9 and 10-12, but not
for dendrimers 13-15, a possible indication of chiral conformational
order in the former two series of dendrimers, but not in the last. How
ever, the optical activities ([Phi](D)) of low-molecular-weight model
compounds 16 (+262) and 17 (+122), prepared to simulate different regi
ons of the dendrimer structure, suggest that as generation size increa
ses slight constitutional changes have a strong effect on the chiropti
cal properties of the dendrimer subunits. Using the [Phi](D) values of
these and other (18-23) low-molecular-weight model compounds, we calc
ulated [Phi](D) values for dendrimers 7-15 that agree within 14% of th
e observed values. Agreement between the optical activity of the model
compounds and the dendrimers leads to the conclusion that the conform
ational equilibria of the dendrimer subunits are not perturbed relativ
e to those of the model compounds. Therefore, we interpreted the chang
e in [Phi](D)/n as dendrimer generation increased for dendrimers 7-12
to be based solely on constitutional changes in the dendritic structur
e and not chiral conformational order.